Is it possible to group several objects and then manipulate them (scale, rotate, translate) as one?
Groups in itself are not that useful. You cannot directly manipulate a group of objects as one object. Although groups make it easier to select objects with Shift + G.

The real power of a group comes from instancing and dynamic linking. Which I will explain:

Instancing:

Once you've created a group, you can instantiate this group elsewhere in the scene by Add>Group Instance. This saves you the trouble of creating literal duplicates of your objects. Consider a city scene, I might have a number of objects that makes up a car model. By grouping these objects into a group, I can place a car group instance anywhere in the scene with very little overhead.

Dynamic Linking:

In many ways, dynamic linking is an extension of instancing. The only difference is that we are using a group from another blend file(often called a library). Dynamic linking is a very useful feature in a large production, because it allows larger scenes to be broken up in smaller chunks. (managed by different people)